Field of Invention
Embodiments of the present invention relate to an acidic gas absorbing agent, a method for removing an acidic gas, and an apparatus for removing an acidic gas.
Background Art
A greenhouse effect through an increase in concentration of carbon dioxide (CO2) has recently been pointed out as a cause of a global warning phenomenon, and an urgent task is to implement an international environment protection measure on a global scale. The emission of CO2 is mainly derived from industrial activity, and a momentum towards the suppression of CO2 emission has been increased.
Techniques for the suppression of an increase in the concentration of acidic gases including CO2 include the development of energy saving products, techniques for the utilization of acidic gases as resources and isolation and storage of acidic gases, conversion to alternative energy such as natural energy and nuclear energy that do not emit acidic gases. Techniques for the separation and recovery of acidic gases being emitted are known as one of such techniques.
Acidic gas separation techniques studied up to now include absorption, adsorption, membrane separation, and cryogenic separation methods. Among them, the absorption method is suitable for massive treatment of gases and is under studies on application to plants and power generation stations.
A method in which combustion exhaust gases that are emitted in combustion of fossil fuels are brought into contact with a chemical absorbing agent to remove and recover CO2 contained in the combustion exhaust gas, and a method that stores the recovered CO2 are known as methods that are mainly intended, for example, for facilities such as thermal power stations using fossil fuels (for example, coal, petroleum, and natural gas). Further, a method in which acidic gases such as hydrogen sulfide (H2S) other than CO2 are removed using chemical absorbing agents has been proposed.
In general, alkanolamines exemplified by monoethanolamine (MEA) have been developed as chemical absorbing agents used in the absorbing method around 1930s and have also currently been used. This method that uses alkanolamines is cost-effective and, further, an increase in size of removing apparatuses is easy.
Alkanolamines used in the absorbing method include monoethanolamine, 2-amino-2-methyl-1-propanol, methylaminoethanol, ethylaminoethanol, propylaminoethanol, diethanolamine, methyldiethanolamine, dimethylethanolamine, diethylethanolamine, triethanolamine, and dimethylamino-1-methylethanol.
In particular, primary monoethanolamines are advantageously high in reaction rate and thus have been extensively used but, on the other hand, suffer from problems of corrosive properties against metals and the like, high susceptibility to deterioration, and high energy required for regeneration. On the other hand, tertiary methyldiethanolamines are advantageously less corrosive and further low in energy required for regeneration but, on the other hand, suffer from a problem of absorption rate. Accordingly, the development of novel absorbing agents that can overcome these drawbacks have been demanded.
In recent years, among amine compounds, particularly alkanolamines having a structural steric hindrance have been studied as acidic gas absorbing agents. The alkanolamines having a steric hindrance are advantageously very high in the degree of selectivity for acidic gases and are low in energy required for regeneration.
A method is known that uses, as the alkanolamine, alkanolamines with branched alkyl groups bonded to a nitrogen atom. As long as the present inventors know, such alkanolamines have a high level of carbon dioxide absorption property, but on the other hand, has an unsatisfactory level of carbon dioxide releasing property and, at the same time, suffer from a problem of a relatively high level of heat of reaction with the acidic gas. On the other hand, a method is also known that uses, as the absorbing agent, cycloamines that are amine compounds having a structure different from that of the alkanolamine compound.